At that point, the A's stood at 66-41, good enough for a two-game lead over the Angels and still the best record in the game.

Flash-forward a month, and Oakland is in a tailspin.

Entering play Monday, the A's have lost four straight—getting swept by the Angels—and six of their last ten. At 78-58, they're five games behind Los Angeles in the AL West.

And the Halos have tied Oakland for the league lead in runs scored, per ESPN.com.

If the season ended today, Oakland would face a one-game, do-or-die wild-card playoff against the Detroit Tigers, a nightmare scenario for a team with designs on a deep October run.

Reinhold Matay/Associated Press

All clubs endure slumps. It's worth wondering, though, if Oakland's malaise can be blamed at least partly on a roster shakeup that didn't need to happen.

In other words: Did general manager Billy Beane, intent on hoisting his first Commissioner's Trophy, fix what wasn't broken?

Certainly no one can accuse Beane of being timid. Here's what MLB.com's Richard Justice wrote about the "Moneyball" GM after the Lester swap:

[Beane] pushed his cards onto the table for 2014. He didn't stop there. He threw in his wristwatch, shoelaces, car keys and Taco Bell card.

All that matters is now. He's nutty in that way, singularly focused. That's what Beane wants his players to know. And his manager. And all the people who care about the A's.

The key, Beane told Justice, is to identify when you have a roster capable of claiming the ultimate prize. "And when you do," Beane said, "you go for it."

Sometimes, though, going for it comes at a price.

That's not to say the chips Oakland acquired haven't contributed. Samardzija owns a 0.965 WHIP as an Athletic, and Lester has posted a 2.66 ERA in 40.2 innings since donning the Green and Gold.

Lester also tossed a complete-game shutout for the A's on August 7, and his playoff pedigree is something Oakland is counting on.

Provided they get far enough to use it.

To net Lester, Oakland gave up Cespedes, a key cog in its MLB-pacing offense.

“My mind is blown,” Oakland outfielder Josh Reddick told SFGate.com's Susan Slusser at the time. “I’m still trying to wrap my mind around this. Never in my wildest dreams did I think we would give up Cespy."

Tom Szczerbowski/Getty Images

Cespedes wasn't the only weapon in Oakland's arsenal. In fact, you could argue that his prodigious pop masked a rather pedestrian .256/.303/.457 slash line.

What's unarguable, though, is that the A's haven't been the same since their midseason shakeup.

Beane recently dismissed the correlation. "I'm happy to have Lester's three wins,'' the GM said, per John Hickey of the San Jose Mercury News. "Those are three wins I don't know we'd have without him.''

Maybe not. But there is an intangible—call it chemistry, call it mojo—that the A's appear to have lost.

They could still find it again; there's a whole month of baseball left.

For now, as they scramble to get back to the top of the heap, the A's are learning change isn't always what it's cracked up to be.